Year	Percent
1991	54.26
1992	54.1
1993	53.95
1994	53.86
1995	53.78
1996	53.74
1997	53.68
1998	53.59
1999	53.53
2000	53.53
2001	53.61
2002	53.59
2003	53.63
2004	53.16
2005	52.85
2006	52.56
2007	52.22
2008	51.85
2009	51.33
2010	50.93
2011	50.72
2012	56.59
2013	48.65
2014	49.8
2015	49.74
2016	50.84
2017	50.99
2018	50.88
2019	50.72